This invention relates generally to high voltage transistor applications and more particularly concerns an improved optically controlled power supply regulator in which an optoisolator transistor is controlled by an input light emitting diode to turn on a series of high voltage MOSFETs for use in applications currently using a high voltage light dependent resistor (LDR) controlled with a light emitting diode (LED).
FIG. 1 shows an existing light emitting diode controlled with a light dependent resistor. A light emitting diode or LED 10 is positioned to shine light rays 12 onto a light dependent resistor or LDR 14. The LDR 14 is mounted on a substrate 16. When the LED 10 shines light rays 12 on the LDR 14, resistance of the LDR 14 changes. The resistance of the LDR 14 is linearly dependent on the intensity of the light rays 12.
Typically, optically controlled power supply regulators utilize a LDR. Unfortunately, the response time of a LDR is long and the device is not stable. In addition, the existing LDRs have a life span of 11/2 year which increases the cost of ownership since the parts have to be replaced frequently. Furthermore, the material (cadmium sulfide) used in the existing LDRs are not environmentally friendly.
U.S. Pat. No. 5,381,018 titled "Electronic Circuit to replace a Light Emitting Diode and a Light Dependent Resistor" has disclosed a circuit which utilizes an optoisolator transistor controlled by an input light emitting diode to replace an existing LDR. In the U.S. Pat. No, 5,381,018, the disclosed circuit is utilized as an optically variable impedance.
In this application, the disclosed circuit of U.S. Pat. No. 5,381,018 is utilized as an optically controlled power supply regulator which is faster than the existing optically controlled power supply regulators with LDR.
However, once the circuit of U.S. Pat. No. 5,381,018 is utilized as an optically controlled power supply and placed on a system board, it shuts down. A system board is a board which is connected to a high voltage power supply to regulate the operation of the power supply in order to deliver proper current and voltage to xerographic process.
Accordingly, it is the primary aim of this invention to provide a replacement circuit for a power supply regulator using LED/LDR device. It is also an object of this invention to provide a replacement optically controlled power supply regulator which is stable, has faster response times, has a long life span, has significantly lower cost of ownership and is environmentally friendly. It is further an object of this invention to utilize the circuit disclosed in U.S. Pat. No. 5,381,018 as the bases for the optically controlled power supply regulator of this invention and improve the subject circuit in order to overcome the shut down problem.
Further advantages of the invention will become apparent as the following description proceeds.